Creaming of synthetic rubber latices



Patented Jan. 22, 1946 STATES CRG OF SYNTHETIC RUBBER LATICES Charles R. Peaker, Union City, Conn, assignor to United States Rubber N. Y., a corporation of New Company, New York,

Jersey No Drawing. Application July 1, 1944, Serial No. 543,197

Claims.

This invention relates to improvements in the creaming of synthetic rubber latices.

Synthetic rubber latices, as is known, may be prepared by the emulsion polymerization in an aqueous medium of butadienes-l,3, or mixtures of butadienes-1,3 with other polymerizable compounds capable of forming copolymers with butadienes-l,3. Such aqueous emulsion polymerizates, or synthetic rubber latices, may be creamed by the addition of a hydrophilic colloidal creaming agent such as a vegetable mucilage, as used for creaming natural rubber latex, which will cause the dispersion on standing to separate into a polymer-rich fraction and a polymer-poor fraction, which fractions may be separated from each other by simple mechanical means, such as decantation, drawing ofi, and the like.

'By the present invention, there is obtained an increase in the concentration of synthetic rubber in the polymer-rich or cream fraction in the creaming of synthetic rubber latices with hydrophilic colloidal creaming agents.

In carrying out the present invention, the creaming operation is carried out in the presence of an alkali silicate in addition to the hydrophilic colloidal creaming agent. The silicate may be added to the emulsion of the monomeric materials before polymerization, or to the completed synthetic rubber latex or emulsion polymerizate. The hydrophilic colloidal creaming agent may be the conventional vegetable mucilages used in the creaming of natural latex, for example, alginates, locust seed or carob bean gum, pectates, Karaya gum, Irish moss, and the like. These vegetable mucilages may be used in amounts between .05 to 1% based on the water phase of the synthetic rubber latex, similarly to the creaming of natural rubber latex. The alkali silicate may be any of the commercial silicates having varying proportions of sodium or potassium oxide to silicon dioxide content. For example, N" brand sodium silicate (Philadelphia Quartz Co.) is sold in the form of an aqueous solution of about 38% solids content, in which ratio NazOzSiOa is about 1:32. U brand sodium silicate (Philadelphia Quartz Company) is sold in the form of a 47% aqueous solution in which the ratio NazOZSiOz is about 122.4. KaSil brand potassium silicate (Philadelphia Quartz Co.) is sold in the form of a 27% aqueous solution in which the ratio K20:Si02 is about 1:25. Various other silicates, such as sodium meta silicate (N2O.Si0z), and ordinary Water glass (NazOASiOz) may be used. The amount of sodium silicate added may vary over wide ranges, as for example, from 2 to 20 parts of alkali metal silicate (solids) per 100 parts of solids of the synthetic rubber latex.

In the preparation of the synthetic rubber latex, as is known, polymerizable monomeric compounds are emulsified in an aqueous medium by means of an emulsifying agent, such as a soap or other surface active agent, and the polymerization is made to take place generally at elevated temperatures in the presence of a catalyst and other regulating materials. Examples of such polymerizable material are the various butadienes-1,3, for example, butadiene-l,3, methyl-2- butadiene-l,3, (isoprene), chlQro-Z-butadiene- 1,3 (chloroprene), piperylene, 2,3-dimethyl-butadime-1,3. The polymerizable material as known may be a mixture of such a butadiene-1,3 with another polymerizable compound which is capable of forming a copolymer with butadienes- 1,3, for example, a compound which contains a GH =C group where at least one of the disconnected valences is attached to an electro-active group, that is, a group which substantially increases the electrical dissymmetry or polar character of the molecule. Examples of compounds which contain a CHFC group and are copolymerizable with butadienes- 1,3 are aryl olefins, such as styrene, and vinyl naphthalene, the alpha methylene carboxylic acids, and their esters, nitriles and amides, such as acrylic acid, methyl acrylate, methyl methacrylate, acrylonitrile, methacrylonitrile, methacrylamide; isobutylene; methyl vinyl ether; methyl vinyl ketone; vinylidene chloride. Present day commercial synthetic rubbers of the above types are polymerized chloro-2-butadiene- 1,3, known as neoprene or GEM rubber, copolymers of butadiene-l,3 and styrene, known as Buna S or GRS rubber, and copolymers of butadiene- 1,3 and acrylonitrile, known as Buna N or GRN rubber.

The following examples are illustrative of the present invention. Each creaming reported in the examples is the optimum of a series of creamings with varying amounts of the creaming agent, whether in the absence of a silicate as in the controls, or with the addition of specified amounts of silicates as in the illustrations of the invention.

Example I A 40% solids Buna S latex was prepared by polymerizing an aqueous emulsion of 50 parts by weight of butadiene-l,3 and 50 parts by weight of styrene in the presence of 5 parts by weight of the potassium soap of wood rosin as an emulsifying agent and small amounts of conventional oxidizing catalyst and aliphatic mercaptan regulator. 2 more parts by weight of the soap were added after polymerization for further stabilizing the latex.

Portions of this Buna latex were creamed with without difliculty. In addition, silicates of relavarious amounts at 2% aqueous ammonium tively high silica content, afte being dried, are alginate solution equivalent to .1 to .5% dry amnot readily redispersed in water, and hence their monium alginate based on the water phase of the presence in a dried film or the synthetic rubber latex, with and without the addition of alkali latex would not contribute to excessive water absilicate. A control series of runs were creamed orption which would be undesirable in many for three days at room temperature (about 21 C.) cases. using the creaming agent alone as in prior prac- Eaample III tice. Three other series of runs were made with a In this case a creammg agent different from the additi n 01' 25 P s Of brand Sodium that of Examples I and II, namely, locust seed silicate solution per 100 pa of latex solidsor carob bean gum, was used. The creaming These were allowed to cream for three days at agent was dissolved in old water to give a 2% room temperature, and at 25 C. and 50 C. reaqueous solution and suflicient of the solution spectively. A further series of three roo was added to give a series of runs having an perature creamings were made with the addition equivalent dry locust bean gum content f about of 15, and 30 parts of N brand sodium silicate to 3% based on the water phase of the latex. solution per 100 parts 0! latex sOlldS. The opti- A l t similar t t of Example I was used mum results are shown in the following table: and the solids content prior to creammg was 35% Parts'qq" brand odium Tempem- Per cent :3: 20 811111 310119 gave Sen-m1 separation a. ili a e solution added tum 32x3 111mm 41.0% total solids cream, whereas the addition of parts of N brand sodium silicate solution per 100 parts solids of the latex gave an optimum g fl g3 serum separation of 26.1% with a total solids 25 3; 50:3 25 cream of 45.8%. It is apparent that the present 2? improvement is applicable to the creaming of 1 3 12 5818 synthetic rubber latices with various conven- 21 tional creaming agents. It is evident from the above table that the addi- Example IV tion or sodium silicate with the hydrophilic col- In this case a different Buna. S latex from that loidal creaming agent increases considerably the of the previous exampl w s se A 26. solsolids concentration or the cream. It is also ids Buna s latex was p epared by polymerizing shown that although the higher temperatures n q e us m i n of 5 pa ts y i ht or may increase the concentration of the cream to dien -L i and 5 parts by weight of styrene amount of silicate added is not critical. mercaptan regulator.

l H 40 The latex was creamed with varying amounts ramp e of 2% ammonium alginate solution equivalent to In a series of creamings on a Buna S latex sim- .1 to .5% dry ammonium alginate based on the ilar to that of Examplelwith ammonium alginate, Water phase of the latex, with and without the were added various alkali silicates. The creamfurther addition of 25- parts of N" brand 38% ings in this and the following examples, except sodium silicate solution per 1 pa t 1 l ex Example V, w r carried gut t room temperature solids. The solids concentration of the latex samfor a sufilcient time to reach equilibrium, gen- D f e cre ming was about 25%. erally about 2 to 3 days. The initial solids of the A further series of runs w also m de n a latex prior to creaming was 36 to 38%, so that th similar latex 01' 25.2% total solids with varying percentag ru parat i each case is t amounts of ammomum alginate and 15, 20 and direct measure of the efficiency of the creaming, Parts respectively of brand 33% Sodium t higher t serum eparation the more m silicate solution. The latex solids before creamcient the creaming and the higher the polymer mg was 22% to content of the cream. Solid concentrations of The results of optmlum creammgs this the various creams in this run were not made. series are in the following table:

1 win Per cent total Per cent Per cent the to] 0 g table Parts N brandsodium solids in serum total solsilicate solution added latex before separaids in Alkali silicate added creaming tlon cream Parts at 24.9 31. 0 3s. 4 was a; a: as latex solids 22 3 54. 5 1 x 22. 9 64. 5 62 6 None won tr ggun a 3 ran so inm s' ca eso u on. 25 35.0 brand sodium Silicate 501mm 20 9 It is evident from the above that a considerable gfi g b potassium i e 34 41 9 increase in the total solids content of the cream rystallinesodiuinnieta 'sii'icHiEfLIIIII 5 41:0 with various Buna S latices is effected by creaming in the presence of sodium silicate,

It is apparent that the various alkali silicates Example V increase the efliciency of creaming of Buna S latices. It is preferred to use those silicates which In this case, the alkali silicate was added to are relatively high in silica content since these the emulsion of monomeric materials before impart only a mild alkalinity to the latex and are polymerization to the Buna S latex. An emultherefore readily added to synthetic rubber latices 76 sion was prepared containing 50 parts by weis of butadiene-1,3 and 50 parts by weight of styrene, dispersed with parts by weight of potassium soap of woods resin in 200 partsby weight of water. and containing small amounts of conventional oxidizing catalyst and aliphatic mercaptan regulator. To a portion of this emulsion of the monomeric materials was added 5 parts by weight of N" brand sodium silicate solution per 100 parts of polymerizable material. To another (control) portion-no silicate was added. Both portions were polymerized 18 hours at 65 0., after which the unreacted butadiene-1,3 and styrene monomers were removed in the conventional manner by venting off the butadiene-1,3 followed by steam distillation of the styrene. In

both cases the conversion to the butadiene-1,3

and styrene copolymer in the latex was 92 to 93% complete. 4

The control and silicate treated portions were creamed at room temperature for 24 hours with varying amounts of 2% ammonium alginate solution equivalent to .1 to .3% dry ammonium alginate based on the water phase of the latex.

The results of optimum creamings inthe two series of runs are shown in the following table:

Per cent total 7 Parts N brand sodium silicate solusolids in laggf g g tion added to: before cream creaming None (control) 10.0 39. 2 5 2i. 6 45. 6

- philic colloidal creaming agents.

Example VI A 42% solids Buna N latex was prepared by polymerizing an aqueous emulsion of 60 parts by weight of butadlene-1,3 and parts by weight of acrylic nitrile in the presence of 7% of the potassium soap of a dehydrogenated, distilled rosin as an emulsifyin agent, and small amounts of oxidizing catalyst and conventional aliphatic mercaptan regulator. In this case the addition of sodium silicate tended to somewhat destabilize the latex and hence the latex was more completely stabilized by the addition of 2 parts of a commercial stabilizer Aquarex D (sodium lauryl sulphate) per 100 parts of the latex.

The latex was creamed with varying amounts of ammonium alginate from .05 to .20% based on the water phase of the latex with and without the addition of 25 parts by weight of "N" brand 38% sodium silicate solution per l00parts of the latex solids.

The results of optimum creaming in the two runs is shown in the following table.

The above shows improvement in the creaming of Buna N latex, even with a relatively high solids content latex as the starting material.

Example VII Per cent total Per cent Per cent Parts N" brand sodium solids in serum 5e total silicate solution added later before solids in creaming cream None (control) 49. 1 22. 3 60. 9 10 48. 0 27. 3 62. 3

The above shows a considerable improvement in the total solids of the cream of neoprene latex even with creaming from a very high initial solids content latex..

The effect of alkali silicates on the creaming of natural-rubber latex is very different from and actually opposite to, the effect of sodium silicate on synthetic rubber latices as exemplified above. Sodium silicate retards the creaming of natural rubber latex with hydrophilic colloidal creaming agents as illustrated in the following:

A 36% total solids natural rubber latex was creamed with varying amounts of ammonium 'alginate from .03 to .10% based on the water phase of the latex, with and without the addition of 15, 25 and 45 parts respectively of N" brand 38% sodium silicate solution per 100 parts of the latex solids. The latex solids before creaming was about 32-33%. The results of optimum creamings, which were all at an alginate concentration of less than the maximum .10% used (showing adequate creaming agent present) are It may be seen from the above table, as distinguished from the case of synthetic rubber latices, the total solids in a natural rubber latex cream is decreased by the presence of sodium silicate in the creaming operation.

In view of the many changes and modifications that may be made without departing from the principles underlying the invention, reference should be made to the appended claims for an understanding of the scope of the protection afforded the invention.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

.1. The improvement inthe creaming with a hydrophilic colloidal creaming agent of a synthetic rubber latex comprising an aqueous soap emulsion polymerizate of polymerizable material selected from-the group consisting of butadiene- 1,3, methyl-Z-butadiene-IB, chloro-2-butadiene- 1,3, plperylene and 2.3-dimethyl-butadiene-l3 polymerizable compounds capable for forming copolymers with butadienes-l,8 which comprises carrying out the creaming operation in the presence of a hydrophilic colloidal creaming agent and an alkali silicate.

2. The improvement in the creaming with a hydrophilic colloidal creaming agent of a synthetic rubber latex compressing an aqueous soap emulsion polymerizate of polymerizable material selected from the group consisting of buta- (Ilene-1,3, methyl-2-butadiene-L3, chloro-2-butadiene-l,3, piperylene and 2,3-dimethyl-butadime-1,3 and mixtures of such butadienes-l,3 with a compound which contains a group and is copolymerizabie with butadienes- 1,3 which comprises carrying out the creaming operation in the presence of a hydrophilic colloidal creaming agent and an alkali silicate.

3. The improvement in the creaming with a vegetable mucilage of a synthetic rubber latex comprising an aqueous soap emulsion polymerizate of a mixture of butadiene-1,3 and styrene which comprises carrying out the creaming Operation in the presence of a vegetable mucilage and an alkali silicate.

4. The improvement in the creaming with a vegetable mucilage of a synthetic rubber latex comprising an aqueous soap emulsion polymerizate of a mixture of butadiene-l,3 and acrylonitrile which comprises carrying out the creaming operation in the presence of a vegetable mucilage and an alkali silicate.

5. The improvement in the creaming with a vegetable mucilage of a synthetic rubber latex comprising an aqueous soap emulsion polymerizate of chloro-2-butadiene-l,3 which comprises carrying out the creaming operation in the presence of a vegetable mucilage and an alkali silicate.

6. A process for treating a synthetic rubber latex comprising an aqueous soap emulsion polymerizate of polymerizable material selected from the group consisting of butadiene-LS, methyl-2- butadiene-l,3, chloro-2-butadiene-L3, piperylene and 2,3-dimethyl-butadiene-L3 and mixtures of such butadienes-l,3 with other polymerizable compounds capable of forming copolymers with butadienes-Ls which comprises allowing such an the group consisting of butadiene-l,3, methyl-2- butadiene-l,3, chloro-2-butadiene-l,3, piperylene and 2,3-dimethyl-butadiene-l,3 and mixtures of such butadienes-l,3 with a compound which contains a group and is copolymerizable with butadienes- 1,3 which comprises allowing such an aqueous emulsion polymerizate containing a hydrophilic colloidal creaming agent and an alkali silicate to stand until it separates into a polymer-rich fraction and a polymer-poor fraction, and separating said fractions from each other.

8. A process for treating a, synthetic rubber latex comprising an aqueous soap emulsion polymerizate of a mixture of butadienes-l,3 and styrene which comprises allowing such an aqueous emulsion polymerizate containing a hydrophilic colloidal creaming agent and an alkali silicate to stand until it separates into a polymer-rich fraction and a polymer-poor fraction, and separating said fractions from each other.

9. A process for treating a synthetic rubber latex comprising an aqueous soap emulsion polymerizate of a mixture of butadienes-1,3 and acrylonitrile which comprises allowing such an aqueous emulsion polymerizate containing a hydrophilic colloidal creaming agent and an alkali silicate to stand until it separates into a polymerrich fraction and a polymer-poor fraction, and separating said fractions from each other.

10. A process for treating a synthetic rubber latex comprising an aqueous soap emulsion polymerizate of chloro-2-butadiene-l,3 which comprises allowing such an aqueous emulsion polymerizate containing a hydrophilic colloidal creaming agent and an alkali silicate to stand until it separates into a polymer-rich fraction and a polymer-poor fraction, and separating said fractions from each other.

CHARLES R. PEAKER. 

